The recipient of Mark Zuckerberg’s latest $1 billion philanthropic contribution is a Silicon Valley institution that primarily feeds other nonprofits working in education, health care and the environment.

But neither the head of the Silicon Valley Community Foundation nor Mr. Zuckerberg would say much about how the new grant will be used.

“We are thrilled that he has chosen us to continue, in partnership, his giving,” foundation CEO Emmett Carson said in an interview. “We respect every donor’s privacy and each donor has their own philosophy and interests.”

In a securities filing Thursday, Facebook said Mr. Zuckerberg would donate 18 million shares to a group the company later identified as the community foundation. At Thursday’s closing price of $55.05, those shares would be valued at $991 million.

Zuckerberg also gave the foundation 18 million Facebook shares, then valued at roughly $500 million, in December 2012. Earlier, he pledged $100 million through the foundation that will eventually go to the public schools in Newark, N.J.

The community foundation, formed in 2007 by the merger of two predecessors, was created to help Silicon Valley companies and their wealthy executives channel charitable contribution to a range of other organizations. Carson said the foundation works with more than 125 corporations and 1,650 smaller charities and issues grants discreetly.

Carson said the group had about $3.5 billion in assets, before Zuckerberg’s planned donation. In 2012, he said about 40% of the foundation’s grants went toward education, 14% toward health causes, and 5% to environmentally focused non-profits.

Kirk O. Hanson, executive director of Santa Clara University’s Markkula Center for Applied Ethics and a consultant to the foundation, said the foundation is a place where Zuckerberg can work with a professional staff and learn how to become a professional philanthropist, said

“If you’re looking to give away half of your wealth, you need expertise on how to do that,” Hanson said in an interview. “No individual philanthropist starts out with that knowledge, and they need help in establishing an infrastructure that will enable to them to give in the most effective way possible.”

Hanson said Zuckerberg is the largest individual donor to the foundation. The second largest giver – having donated about $500 million – is Jeff Skoll, the first employee and first president of eBay, Hanson said.

Community foundations are popular targets because they allow donors to shield the ultimate recipients of their largesse, said Melissa Berman, an adjunct professor at Columbia University who teaches courses on philanthropic strategy.

“Using a community foundation is like this gives people like Zuckerberg and his wife more privacy in their giving,” Berman said. Such groups have to say where their money goes, but not where it came from or who directed which grants go where, she said. “This allows people to give essentially in secret, and that’s attractive to people in the spotlight.”

Carson said he is grateful for the gift on any terms. “I think this serves as a testament to the giving nature of Silicon Valley, and I think this will help inspire others to give as well,” he said.